REACTIONS OF MELANOPHORES OF AMBLYSTOMA 259 



to light are in most cases adaptive. The primary reaction of the 

 melanophore is to expand when illuminated which it always 4oes 

 when directly stimulated with light of ordinary intensity and 

 sometimes when the stimulus is indirect and through the eyes. 

 Fuchs (p. 1651) closes his review of the color changes of the 

 reptiles with the statement that in those animals which do not 

 show expansion of the pigment in the light, either the parietal 

 organ has lost its function in the course of phylogeny or ontogeny, 

 or the eyes have gained a regulatory influence over the light 

 reactions which results in changing the original light reaction 

 (expansion) into the directly opposite reaction (contraction). 

 1 should change this statement and applying it to the chromato- 

 phores of all animals say, that in those animals in which the 

 pigment cells do not expand in light of ordinary intensity and 

 under normal conditions of temperature but contract, this is due 

 to the controlling regulatory influence of the eyes, by means of 

 which the reactions of the melanophores are made adaptive. In 

 other words, when the pigment cells contract in the light, this 

 reaction is one that is bound up with the nervous system in that 

 an impulse started in the retinae is sent out which is opposite 

 to that produced by direct stimulation. Such is the case in 

 frogs, in Diemyctylus, and in Phoxinus, Salmo, etc. Usually, 

 however, the melanophores expand in the light, due in most 

 part, to their direct stimulation, although the eyes still show an 

 influence in that in many cases the expansion is not maximal 

 as it is when the eyes are removed, and that when the eyes are 

 present the reactions come about more quickly. 



SUMMARY 



1. The epiphysis of Amblystoma punctatum larvae has no 

 influence on the reactions of the melanophores to light and 

 darkness. There is no parietal organ. 



2. The view is expressed that the reaction to light of ordinary 

 intensity of the pigment cells in the skin of animals is to expand. 

 When this does not take place it is due to the controlling regula- 

 tory influence of the eyes. 



